1. Field of the Invention
This invention relates to a backlight apparatus and a color image display apparatus wherein a color display panel is illuminated from the back side.
2. Description of the Related Art
Very thin television receivers formed using a liquid crystal display (LCD) or a plasma display panel (PDP) in place of a cathode ray tube (CRT) which has been used for long years after television broadcasting was started have been proposed and placed into practical use. Particularly, a liquid crystal display apparatus which uses a liquid crystal display panel is advantageous in that it can be driven with low power consumption and can be formed as a large size display unit. Therefore, the liquid crystal display apparatus is estimated to be popularized progressively together with reduction of the price of a large size liquid crystal display panel, and further development in future of the liquid crystal display apparatus is anticipated.
Among color liquid crystal display apparatus, a color liquid crystal apparatus of the backlight type wherein a transmission type color liquid crystal display panel having color filters is illuminated from the back side by a backlight apparatus to display a color image has become the main current. For the light source of the backlight apparatus, a fluorescent lamp such as a cold cathode florescent lamp (CCFL) which uses a fluorescent tube to emit white light is used frequently.
Since the CCFL uses mercury enclosed in the fluorescent tube, it may possibly have a bad influence on the environment. Therefore, a light emitting diode (LED) is estimated hopeful as the light source for a backlight apparatus in place of the CCFL as disclosed, for example, in Japanese Patent Laid-Open No. 2001-142409 (hereinafter referred to as Patent Document 1).
As a result of development of a blue light emitting diode, light emitting diodes which emit red light, green light and blue light of the primary colors of light have become complete. By mixing red light, green light and blue light emitted from the light emitting diodes, white light having high purity of white can be obtained. Accordingly, where the light emitting diodes are used as a light source for a backlight apparatus, after the light from the light source passes through the liquid crystal display panel, resulting color light has high color purity. Therefore, the color reproduction range can be widened significantly when compared with that by the CCFL.
For the light emitting diodes to be used as a light source for a backlight apparatus, light emitting diodes which use a light emitting diode (LED) chip of a high output are used effectively. Where light emitting diodes of the type mentioned are used, the luminance of the backlight apparatus can be enhanced significantly.
Incidentally, in a color liquid crystal display apparatus of the backlight type, a color liquid crystal display panel upon which prescribed white light is illuminated from the back side by a backlight apparatus shades the white light to extract only light of an object color component for each pixel by means of color filters to display a color image.
In particular, from within the white light emitted from the backlight apparatus, only light of an object color component extracted through the color liquid crystal display panel is utilized. For example, in order to display the entire screen in red, the color liquid crystal display panel shades the white light at those pixels other than pixels for which the red filter is provided, that is, at those pixels for which the green filter and the blue filter are provided. Therefore, light of the pixels other than the pixels for which the red filter is provided is not utilized.
In this manner, in existing color liquid crystal display apparatus of the backlight type, since white light including color components which are not utilized is emitted from the backlight apparatus, power is consumed uselessly as much.
Therefore, the assignee of the present invention has proposed, in Patent Document 1 mentioned above, an apparatus and method wherein a backlight panel is driven in a unit of a divisional region from among a plurality of divisional regions and the luminance of the backlight is controlled in response to an image signal to reduce the power consumption.